A heat treatment technique is a fundamental and important technique which has been used for various semiconductor processes. For example, the heat treatment is performed on a silicon single crystal wafer used as a semiconductor substrate to modify a crystal quality, diffuse impurities, or form a film structure in a surface layer portion.
As a heat treatment apparatus for performing a heat treatment, a batch type apparatus capable of simultaneously processing multiple wafers at predetermined intervals has been widely used. In particular, an apparatus in which wafers are placed in a vertical direction while holding each wafer horizontally is called a vertical furnace. An apparatus in which wafers are placed in a horizontal direction while holding each wafer nearly upright is called a horizontal furnace.
The vertical furnace is often used for wafers which progress toward having larger diameter in recent years. A supporting member for holding wafers in the heat treatment furnace is also referred to as boat, and a boat made of quartz (quartz boat) and a boat made of SiC (SiC boat) in which the surface of SiC material is subjected to CVD-SiC coating are generally used.
Especially, a SiC supporting member, which has high resistance to heat, has been widely used in a heat treatment at high temperature. The supporting member varies in shape. A common supporting member for the vertical furnace has three or four vertical columns coupled by two plate members (a top plate and a bottom plate), and grooves are horizontally formed on parts of the columns. Wafers are placed on horizontal planes of the grooves and thereby held.
The silicon single crystal wafers placed on such a supporting member are subjected to a heat treatment, for example, under an argon or oxygen atmosphere. It has been known that a defect called slip dislocation is generated from a contact portion with the supporting member in this heat treatment (see Patent Document 1 and Patent Document 2).